The present invention relates to exothermic welding and improved assemblies and methods therefor.
Exothermic welding has been employed in the past as an effective method of welding two or more members together which may be copper and/or steel, such as cables to cables, cables to ground rods, cables to steel surfaces including plates and pipes, cables to bus bars, cables to rebar and the like. Such exothermic welding eliminates the need for an outside source of heat or power and produces a permanent, corrosion resistant weld which cannot loosen and does not increase electrical resistance.
To accomplish such welds the members to be welded together are positioned adjacent to each other utilizing a welding cavity in a mold formed of a material, such as graphite, which is capable of withstanding the extremely high temperatures of the exothermic welding process. Another ignition cavity in the mold contains a loose particulate weld metal which is to be ignited to initiate the welding process. A metal disk, which typically is a tin plated steel, is first positioned in the ignition cavity to prevent the loose particulate weld metal from flowing into the welding cavity in which the materials are to be welded together prior to ignition. The loose particulate weld metal is then poured from a container, e.g. plastic, into the ignition cavity, the plastic container is discarded and the mold cover is closed. In order to initiate ignition, a spark generator ignites the loose particulate weld metal which melts in the ignition cavity to melt the metal disk and the molten weld metal flows from the ignition cavity into the weld cavity to weld the members together.
The particulate weld metal in exothermic welding is a mixture of copper oxide and aluminum which, when ignited, produces the following chemical reaction3Cu2O+2Al→6Cu+Al2O3+heat (4600° F.).
In order to initiate ignition by spark, the container in which the particulate weld metal is shipped usually contains two different particle grain sizes of weld metal. A finer grain size of weld metal is first packed at the bottom 1/10 or so of the container, and the remainder of the container is then filled with a courser grain size weld metal. Thus, when the particulate weld metal is poured from the container into the ignition cavity in the mold, the courser size weld metal flows first from the container into the cavity, and then the finer grain size weld metal flows on top of the courser grain size, whereby the finer grain size weld metal which is more easily ignited is exposed and presented to the spark to initiate ignition of the entire quantity of both fine and course grain size particulate weld metal.
It would be desirable to be able to eliminate the finer grain size particulate weld metal and only utilize a single uniform courser grain size for several reasons. One reason is the added expense involved in providing two grain sizes and packing the two different grain sizes in the container. Even more significantly, special shipping restrictions apply in the case of the finer grain weld metal because it is more susceptible to ignition than the courser grain particulate weld material.
It would also be desirable to eliminate the need for the tin plated steel disk which must first be inserted in the ignition cavity to retain the loose particulate weld material in the cavity prior to ignition. This would eliminate the need for the separate disk insertion step, the need to provide a disk at all, and would result in cleaner welds and cleaner molds after the welding procedure has been carried out.
It would also be desirable to eliminate the need for the plastic container from which the particulate weld metal is poured into the ignition cavity and the cumbersome step of having to pour the loose particulate weld material into the cavity and the need to dispose of the plastic container.
A smokeless exothermic welding procedure is currently available for exothermic welding in clean room environments. In such smokeless procedure a filter is employed with the mold to trap most of the emissions created in the exothermic welding process while allowing the heated air to escape through the filter. In the smokeless procedure the particulate weld material is ignited electrically by a battery powered ignitor. The electric ignitors in the smokeless procedure eliminate the need for the finer grain more easily ignitable weld metal. However, the smokeless procedure which has been employed in the past has not attained the other desirable goals heretofore described.
In the present invention the need for the finer grain more easily ignitable weld metal is not only eliminated, but the need for the tin plated steel disk as well as the plastic container for the particulate weld material is also eliminated together with the steps of inserting the steel disk in the mold cavity and the need to pour the loose particulate weld material from the container into the ignition cavity. All of these desirable goals are achieved in the present invention while enjoying cleaner molds following a welding procedure as well as cleaner welds.
In one principal aspect of the present invention, an exothermic welding assembly comprises a mold formed of a material which withstands exothermic welding temperatures. The mold has a first cavity therein for positioning at least two members which are to be exothermically welded together adjacent to each other, and a second cavity communicating with the first cavity. A weld metal cartridge is positioned in the second cavity. The cartridge includes a container having a top, a side wall and a bottom wall, with the side wall and bottom wall defining a chamber, a particulate weld metal in the chamber, and a cover covering the top and retaining the particulate weld metal in the chamber. An igniter including an electrical conductor extends into the mold, and a tip on the igniter extends into the particulate weld metal to ignite the weld metal in the chamber of the container.
In another principal aspect of the present invention, a method of exothermic welding comprises the steps of providing a mold formed of a material which withstands exothermic welding temperatures. The mold has a first cavity therein for positioning at least two members which are to be exothermically welded together adjacent to each other using the first cavity. A weld metal cartridge is positioned in the second cavity. The cartridge comprises a container having walls which define a chamber therein, and a particulate weld metal in the chamber. The tip of an electrical igniter is positioned into the chamber of the container and particulate weld material therein, the igniter is electrically fired while the container is in the second cavity of the mold to melt the particulate weld metal, and the contents of the second cavity after melting of the particulate weld metal are passed to the first cavity to weld the members together.
In still another principal aspect of the present invention, in the aforementioned assembly and method the particulate weld metal is a mixture of copper oxide and aluminum.
In still another principal aspect of the present invention, in the aforementioned assembly and method the walls of the container are metal, and preferably copper.
In still another principal aspect of the present invention, in the aforementioned assembly and method a cover is on the chamber, and preferably the cover is a film and/or cap.
In still another principal aspect of the present invention, in the aforementioned assembly and method the igniter tip is positioned in the particulate weld metal in the chamber by puncturing the cover on the chamber.
In still another principal aspect of the present invention, in the aforementioned assembly and method the mold includes an opening communicating between the exterior of the mold and the second cavity, and the igniter tip is inserted through the opening to puncture the cover on the chamber.
In still another principal aspect of the present invention, in the aforementioned assembly and method the mold includes an opening communicating between the exterior of the mold and the second cavity, and the igniter tip is inserted through the opening to position it into the chamber of the container and the particulate weld material therein.
In still another principal aspect of the present invention, in the aforementioned assembly and method the igniter tip is stainless steel or tungsten.
In still another principal aspect of the present invention, in the aforementioned assembly and method the particulate weld metal is of substantially uniform particle size throughout the chamber, and the tip of the electrical igniter is positioned in the substantially uniform particle size particulate weld metal.
These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.